The present invention relates to free piston internal combustion engines and, more particularly, to free piston internal combustion engines having a reciprocating piston rod providing output power.
Internal combustion engines typically include a plurality of pistons which are disposed within a plurality of corresponding combustion cylinders. Each of the pistons is pivotally connected to one end of a piston rod, which in turn is pivotally connected at the other end thereof with a common crankshaft. The relative axial displacement of each piston between a top dead center (TDC) position and a bottom dead center (BDC) is determined by the angular orientation of the crank arm on the crankshaft with which each piston is connected.
A free piston internal combustion engine (FPE) likewise includes a plurality of pistons which are reciprocally disposed in a plurality of corresponding combustion cylinders. However, the pistons are not interconnected with each other through the use of a crankshaft. Rather, each piston is typically rigidly connected with a plunger rod which is used to provide some type of work output. In a free piston engine with a hydraulic output, the plunger is used to pump hydraulic fluid which can be used for a particular application. An example of a free piston internal combustion engine with a hydraulic output is disclosed in PCT publication number WO 93/10342 (Achten et al.), published May 27, 1993.
One possible use for an FPE as described above is for a prime mover in a motor vehicle. It is also known to provide a motor vehicle with an electric motor as a prime mover. Some motor vehicles are configured as hybrid electric vehicles including both an internal combustion engine as well as an electrical power source for powering the electric motor. The internal combustion engine in such a hybrid vehicle is typically in the form of a crankshaft engine, while the electric power source is in the form of a plurality of batteries or fuel cells. Output power in the form of a crankshaft internal combustion engine or batteries has inherit operational inefficiencies.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the invention, a free piston internal combustion engine is provided with a combustion cylinder, a piston reciprocally disposed within the cylinder, and a piston rod coupled with the piston. A linear electrical generator/motor includes at least one magnet carried by the piston rod and at least one coil positioned in association with the at least one magnet. An electrical circuit is coupled with each of the at least one coil and a battery.
In another aspect of the invention, a method of operating a free piston internal combustion engine is provided with the steps of: providing a combustion cylinder, a piston reciprocally disposed within the cylinder, and a piston rod coupled with the piston; providing a linear electric generator/motor including at least one magnet carried by the piston rod and at least one coil positioned in association with the at least one magnet; providing a battery and a capacitor; coupling the at least one coil with at least one of the battery and the capacitor to move the piston during a compression stroke of the piston; and coupling the at least one coil with the capacitor during an expansion stroke of the piston.